fix undefined range for writeFile - test with ods as said in #1914

This FIX

function decode_range(range) { var x = (range||"A1A1").split(":").map(decode_cell); return {s:x[0],e:x[x.length-1]}; }

You are right correction doesn't fit LibreOffice behaviour. So I will propose another Fix :-)

LibreOffice Sheet with empty table : content.xml extract

<table:table table:name="test1_libreOffice" table:style-name="ta1">
    <table:table-column table:style-name="co1" table:default-cell-style-name="Default"/>
<table:table-row table:style-name="ro2">
<table:table-cell/>
</table:table-row>
</table:table>

LibreOffice Sheet with one element in table : content.xml extract

<table:table table:name="test2_libreOffice" table:style-name="ta1">
   <table:table-column table:style-name="co1" table:default-cell-style-name="ce1"/>
       <table:table-row table:style-name="ro1">
       <table:table-cell office:value-type="string" calcext:value-type="string">
           <text:p>merde</text:p>
       </table:table-cell>
    </table:table-row>
</table:table>

SheetJS writed file with my correction for an empty sheet :

    <table:table table:name="test1_sheetJS_ods">
        <table:table-row>
          <table:table-cell />
        </table:table-row>
      </table:table>

SheetJS writed file with my correction for an one cell sheet +1

<table:table table:name="test2_sheetJS_ods">
     <table:table-row>
          <table:table-cell />
         <table:table-cell office:value-type="string"><text:p>TOIP</text:p></table:table-cell>
          <table:covered-table-cell/>
          <table:table-cell />
    </table:table-row>
</table:table>

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